Thermionic tube



March 26 1935- J, v. cAPlcoT-ro THERMIONIC .TUBE

Filed June 7, 1932 INVENTOR James V'gvzw BY ufff/@mum ATTORNEY PatentedvMar; 26, 1935 UNITED STATES PATENT OFFICE THERMIONIC TUBE Y of DelawareApplication June 7, 1932, serial No. 615,796v

` Claims.

This invention relates to improvements in thermionic tubes of theindirect heated cathode type and has for an object the production ofsuch a tube of comparatively small'size suitable for use 5 in smallradio receivers of the midget type. The bulb need not exceed 2" inlength and 3A" in diameter, the tube having Apractically the same outputand other electrical characteristics as a tube of standard size.

Another object of the invention is to provide a special form of cathode,generally applicable to thermionic tubes of this type. This-cathodearrangement and assembly secure ample emission, yet the assembly may berelatively small in size, thus enabling a miniature ampliiier ordetector tube to be produced of similar characteristics to tubes ofstandard size.

A further object of the invention is to provide an inexpensive, compactand efficient construction and arrangement of the electrodes or elementsin a` thermionic tube that will withstand roughy handling in assemblyand use.

Although the invention will `be such details v.are not intended to belimitative of the invention except in so far as set forth in theaccompanying claims. o

In the accompanying drawing where by way of illustration is shown aminiature thermionic tube corresponding to the well known 227 type,embodying the objects of the invention as above set forth: 1

Figure 1 is a vertical sectional view through the tube; Y y

Figure 2 is a vertical sectional view on the line 2--2, Figure 11;

Figure 3 is a horizontal sectional view on the line 3 3, Figure 1; and yFigures 4 and A5 are-views partly in section of the cathode assembly ofthe tube.

The numeral 10 denotes the usual glass bulb having the usual reentrantstem 11 sealed therein containing the usual press in which the circuitconnections and supports for the elements of the tube are sealed. Thebase (not shown) of the tube may be of any suitable constructionprovided with circuit terminals for the tube .electrodes and is securedto the bulb in the usual manner.

The support 12 (which may form one circuit connection of the heaterelement) is sealed into the stem and has an enlarged portion 13 whichsupports an insulating bushing 14, the support passing through thebushing (which may be a tight rit thereon) and having attached to itsinner disclosed in connection with the speciiic details of a preferredyembodiment thereof, it must be understood that.

(Cl. Z50-27.5)

end the lower end 15 of the heating element 16. The heating element orfilament 16 may be of any desired form, but preferably is wound in a`comparatively tight helix andfafter its lower end 15 is attached to thesupport 12, the tube 17 (pref- 5 erably of nickel)A constituting thecathode of the thermionic tube is placed over the lament, the' lower endof said cathode tube being positioned on and preferably tting tightly onthe shoulder 18 of lower bushing 14. The outer surface of 17 can 10 betreated or coated inr any known manner 'if necessary to increase theelectron emission.

Thelament 16 is now extended by pulling it upwards and the upper end 19of same is oon-` nected to member 20. The upper insulating bush- 15 ing21 is slipped over the member 20 and an enlargement 22 is formed on 20which prevents the parts from falling apart during assembly. l

i It Awill be observed from Figure 4 that the ilament 16 may be extendedand has a springlike action and accordingly the shoulder 23 ofthe upperbushing 2l can be brought down and into the bore of the tube 17 and theventire cathode assemblywill be held together by reason of the shoulders'18` and 23 on the bushings which can be made to i'lt tightly within thebore of the tube 17.

The cathode assembly made in the manner just described is shown partlyin section in Figure 5 from which it will be observed that the lament 16is held in tension between the support 12 and the member 20 adjacent to,but out of contact withthe inner walls of the cathode tube 17, andadapted to heat the cathode. It is not therefore necessary `to coat theinterior of this tube with an insulating material or to spray thefilament helix with insulating Amaterial or to mount the filament helixon a center tube of insulating material in order to keep the filament 16from electrical contact with the tube as is the case with knownconstructions. y

The 'cathode assembly being made up and mounted in the center of thetube, the grid is now placed in position about the cathode tube 17 ofthe heater assembly. This grid structure comprises a coil 24 of wireconstituting the grid element or electrode, each turn of the coil beingwelded as indicated at 25 to a support 26 which is sealed in the stem 1land also forms the grid circuit connection. By welding each turn of thegrid coil to its support, it is possible to secure a rigid gridassembly, the coils of which will be properly spaced from and concentricwith the cathode tube 17, and which cannot contact therewith incase theentire tube is roughly handled in shipment or use. 55

Sealed into the stem 11 are the supports 27 and 28, either one of whichmay form the circuit connection to the anode or plate element of thetube. 'I'his is composed of two sections shown at 29, 29a in Figure 3which surround and are welded to the supports 27, 28 in any suitablemanner. Thus the plate elements form what is practically a cylindersurrounding and concentric with the grid and cathode, and this plateassembly is rigidly held against contact with the grid assembly.

An insulating member 30 which may be of mica or the like, has a centralaperture adapted to surround the upper portion of the outer bushing 21of the cathode assembly and is also apertured to receive the upper end31 of the grid support 26. The member 30 is secured to the platesupports 27 and 28 in any suitable manner, and serves to space thecathode, plate and grid assemblies apart from each other and definitelyposition the outer ends of the supports 26, 27, 28.

Extending downwardly through 30 is the connecting rod 32 which is weldedand thereby electrically connected to the member 20. This rod 32 carriesas its lower extremity the button 33 for the getter commonly employed inthermionic tubes. The portion 34 of rod 32 extends laterally as shown inFigure 2 and connects to a circuit connection 35 which together with thesupport 12 may constitute the circuit connections to the heater lament16.

As the iilament 16 is under considerable tension, it may sag in servicewithout coming in contact with the inner walls of the cathode tube 17and the connecting rod 32 is resilient and so ten- .sioned duringassembly that it will pull outwardly against the filament and take upthe slack therein when the lament coil expands when heated, therebyalways keeping the filament out of contact with the inner wall of 17.The member 20 fits rather loosely in the hole in bushing 21 so that thespring action of rod 32 can act on the filament and keep it from saggingwhen hot, and the rod 32 may be free in member 30 or may ilex thismember sufliciently to act in the manner described. When the member 30is made liexible it can act as a spring or tension member, and throughrod 32 act to keep the lament taut.

The integral outwardly extending tab 36 on the cathode tube 17 is bentas shown in Figures 1 and 2 and is connected to the circuit connection37.

The evacuation, sealing and other details of construction of thisthermionic tube not herein described in detail may be carried out in theusual manner, and this tube may be employed for a large variety ofpurposes for which thermionic tubes are commonly used. As the operationof a tube of this character is Well known it is not herein described indetail.

A miniature tube of this character can be used in many applicationswhere standard size tubes cannot be used because of lack of room, forexample, in mantel clock radio receivers where the cabinet contains aclock with a dial and there are 6 tubes in the radio receiver built intothe cabinet and the latter is only 6 x 6 x 10".

What is claimed is:

1. In a thermionic tube having a reentrant stern, a plurality ofsupports having their inner ends sealed into said stem and extendingoutwardly therefrom, a heater assembly having a tubular member andinsulating caps thereon supported on one of said supports, a grid andanode carried by said supports, and an insulating member embracing oneof said caps and the outer ends of said supports for the grid and anode.

2. In a thermionic tube, a. cathode assembly comprising a tubularcathode and means within said cathode for heating the same, said tubehaving insulating heads and being supported in the center of said tube,a grid and plate surrounding said assembly, an insulating member adaptedto prevent lateral movement of said cathode assembly in said thermionictube and embracing one of the insulating heads thereon, and a springtension member passing through said insulatingv member and adapted tohold said heating means in said cathode under tension during operationof the tube.

3. In a thermionic tube, a cylindrical plate assembly, supports thereforsealed into the press in said tube and extending above said plateassembly, a cathode assembly including an insulating cap on the cathode,said assembly being positioned within said plate assembly, and aninsulating member extending across and laterally embracing theinsulating cap of said cathode assembly and secured to said supports.

4. In a thermionic tube, a grid comprised of an open helix of wirehaving each turn thereof secured to a common support, a tubular cathodelying entirely Within said helix, said cathode having insulating caps onits ends extending outside said helix, and means for positioning saidcathode within said tube concentric to said grid and holding the samexed relative thereto including a laterally extending insulating memberembracing one of said caps and said grid support.

5. In a thermionic tube, a cathode assembly comprising a tubularcathode, a heat element therein, insulating heads for said tube, asupport rigidly secured to one of said heads and connected to saidheater element, spring means passing through one of said heads andconnected to said heater element whereby the same is kept stretchedwhile heated, said means forming a circuit connection to said heater,and a getter button supported on said spring means.

JAIVIES V. CAPICOTTO.

